Looking for opinions on 2.93 final drive vs 3.46?

[dadsbmw]

So I've been S52 swapped now for a couple years with the accompanying ZF 5-speed trans and 3.46 LSD diff. I love the gearing for the street, as I get to row through the gears and have some good fun, but cannot stand the ~4k rpm freeway cruising at 80mph. I've been thinking about going 6-speed to add that cruising gear in there, but it's a good chunk of change and work to make that happen. The other option at my disposal is to drop to a 2.93 diff to bring the cruising gear into the same realm of rpm. The issue here, of course, being that the rest of my gears would be taller as well. Curious if anyone out there with S52, ZF, and 2.93 can provide insight into how they like this setup?

There's actually a guy here locally selling a 2.93 LSD as well, but with E30 taxes sky high he's asking $525. These things used to have a hard time commanding much more than $200, so I'm a little wary of spending that much just for an experiment.

Let me know what you all think!

[mtech325]

I think the 2.93 is going to feel extra tall coming from a 3.46 unless you do a lot of freeway driving. To be fair, the 328 e36 and non-zhp 330 5-speed cars had the ZF with a 2.93 final drive. The 6-speed does have its merits though, especially these days with the cost of the 5-speed transmissions and differentials getting extra expensive. Figure you'd need the 6-speed transmission (Getrag or ZF), clutch/flywheel, custom trans mount, and shorten the ZF driveshaft etc., but the shift linkage can be made simpler with a top-mount style to eliminate the need for a custom carrier. Then sell the ZF 5 speed to recoup a few bucks.

Another option is to look for a 3.07, 3.15, or 3.25 differential if you want to keep the 5 speed. I have 3.25 with my ZF car and 80mph is around 3600-3700rpm or so. It's a little annoying, but I don't mind it as much now that I have a quieter exhaust setup.

[RenaissanceMan]

So I can probably speak to this, as my car is equipped with an S52, ZF, and 2.91 LSD now... When I first did my S52/OBDII swap I was using a Metric Mechanic built 3.46 LSD in the car that was previously on my e30/M52 racecar. The car pulled like crazy and was a blast on back roads, but highway driving was a nightmare at any speed over 70. Finally got sick of it and decided to swap. Found a 2.91 LSD (I believe these came from E36 328i sport models..?) and refreshed it before swapping out. IMHO, is it a great compromise. Highway driving is SO much better now and the car still pulls nicely. Maybe not quite as 'fun' as the 3.46 but way more usable overall. You are still going to blast through 1st gear but the overall taller gearing is advantageous in different contexts. Also if you are into timing 0-60 sprints you can do it without having to shift into 3rd gear. I don't really care as much about that, but I suppose it's worth mentioning. If you have any other questions about my build or my experience with the swap just let me know!

[e30austin]

i think the 3.25 is the perfect balance between the two, particularly if you drive on the highway.

[dadsbmw]

So I can probably speak to this, as my car is equipped with an S52, ZF, and 2.91 LSD now... When I first did my S52/OBDII swap I was using a Metric Mechanic built 3.46 LSD in the car that was previously on my e30/M52 racecar. The car pulled like crazy and was a blast on back roads, but highway driving was a nightmare at any speed over 70. Finally got sick of it and decided to swap. Found a 2.91 LSD (I believe these came from E36 328i sport models..?) and refreshed it before swapping out. IMHO, is it a great compromise. Highway driving is SO much better now and the car still pulls nicely. Maybe not quite as 'fun' as the 3.46 but way more usable overall. You are still going to blast through 1st gear but the overall taller gearing is advantageous in different contexts. Also if you are into timing 0-60 sprints you can do it without having to shift into 3rd gear. I don't really care as much about that, but I suppose it's worth mentioning. If you have any other questions about my build or my experience with the swap just let me know!

This is exactly what I was looking to hear. I do enjoy the fun of the low gearing, but I'd say I do about 50/50 city/freeway and it's just a constant feeling of annoyance on the freeway. I also think I need to get more on board with this car being a cruiser more than a powerhouse. I have a 500+hp car for that, and the e30 will never keep up.

Do you mind if I ask when you bought the 2.91 and how much you paid for it?

[dadsbmw]

i think the 3.25 is the perfect balance between the two, particularly if you drive on the highway.

Feel like anything higher than the 2.93 won't be worthwhile enough to make the change.

[RenaissanceMan]

Do you mind if I ask when you bought the 2.91 and how much you paid for it?

Sure thing. I purchased in July 2018 for around $250 I think... Unfortunately I forgot to mark the price I paid in my build spreadsheet. :(

[pazi88]

Feel like anything higher than the 2.93 won't be worthwhile enough to make the change.

Yeah. 2.93 is good compromise. Anything shorter gets annoying at regular driving. I personally have 2.65 ratio and loving it. But I have m52 turbo with 500whp so it's not fair comparision to NA engine.

[Northern]

I ran a 3.73 for years with my M52/ZF5 and I hated it. Last year I finally swapped in an s2.93 and I enjoyed it, I didn't find it too tall or anything.
For a car that is primarily weekend/autox use, sure I see the benefit of a ~3.25. If you do any highway driving, you're going to appreciate the 2.93.

[Panici]

Weighing in here as well, since I will have the M52/ZF combo in both my E36 and E30 shortly.


E36:
My current daily driver is an E36 with a mostly stock M52/ZF320 & 3.91 open diff.
It's amazingly zippy around town and fun for 0-60 runs.
My top speed is also gearing-limited and not power-limited. Certainly gets the blood flowing hitting the 7200rpm limiter in 5th gear!

Unfortunately the (almost) straight-piped exhaust makes highway cruising @ 4000rpm painful without earplugs.
It can be done if your exhaust is more conservative (or you don't mind wearing hearing protection like me).
Although I imagine the engine life will be negatively affected revving that high all the time.


E30:
I'm currently swapping the transmission from a G260 to a ZF320 in my E30.
I will be changing my 3.73LSD to a 2.79LSD I'm currently refreshing.
Not overly concerned with the longer ratios as the M52 is going back in the car with a big turbo attached this time!

For an N/A application something a little shorter then a 2.79 would be a better compromise.

[Chilezen]

I don't like my 3.15 because I think it's too annoying on the freeway. I would happily install a 2.93 or 2.79 if I could get my hands on one. I don't see how some people with anything higher than a 3.15 can tolerate it.

[cdl723]

I have a Zf/3.07 and have no reference other than a 4.1/G260. The 3.07 feels like a decent compromise. I would like to get a 3.25 as 1/2/3rd feel a little too long, but the 3.07 also isn't the best on the interstate ~3500 @ 80mph.

I feel like a 3.25/3.38/3.46+6 speed (3100-3300rpm @ 80mph) would be the best with an S52.

[reelizmpro]

I run 3.15/3.23/3.25 on my S52 swapped cars. 3.23LSD in there currently is from the MZ3 S52 and is perfect IMO but pricey these days. The other alternatives 3.15 Z3 Torsen and 3.25LSD is more common and can be found for less money. These days, it's more about whatever you can find for a good price.

[dadsbmw]

I've decided to stay with the 3.46 for now, as I don't want to lose the acceleration. I'm starting to slowly lean towards turbo in the future, so when that time comes I'll certainly look to move to something much taller.